Kinetic modelling of photomineralization of phenol, as model molecule of aromatic micropollutants, and validation of a photochemical reactor based on photocatalytic membranes immobilizing titanium dioxide and promoting photocatalysts

In the present work, a validation study was carried out in a pre-industrial pilot plant equipped with 9 photocatalytic membrane modules and capable to treat 350-400 L per day. Aq. solns. contg. 4-1,000 pm of phenol, expressed as total org. carbon (TOC), were treated in the plant, and followed kinetically for TOC decrease, as well as for decrease of concn. of substrate, as a function of time, by varying only the kind of oxygen donor (stoichiometric H2O2 or O3) and concn. of a synergic mixt. of tri-(t-butyl)- and tri- (i-propyl) vanadate (V) as photopromoter (added to the membrane during its manuf.). All other parameters of the plant have been optimized in preceding studies. Kinetic modeling was carried out as described in preceding papers of this series. The system of 3 equations and 4 unknown parameters (the "true" k and K couples for substrate and intermediate) was thus solved by successive steps. The final result was a graphical output of curves of substrate, intermediate and carbon dioxide concns., as a function of time, all expressed in terms of carbon content, fitting the exptl. data very satisfactorily. The photocatalytic activity of trialkyl vanadates was evaluated from quantum yields at "infinite" concn., as a function of concn. of photopromoter in the membrane. When using O3, at about 7 wt.% of photopromoter, a more than five-fold quantum yield was obtained. This behavior is discussed on the basis of scavenging of conduction band electrons, by producing ×O2H/×O2- radical species, as well as by dark catalysis and/or photolysis of O3 adsorbed on the TiO2-photopromoter system.